Injection molding apparatus



M. D'AMORE INJETION MOLDING APPARATUS Aug. 24, 1954 4 Sheets-Sheet lFiled July 7, 1949 Aug. 24, 1954 M. D-AMRE 2,686,934

INJECTION MOLDING APPARATUS Filed July 7, 1949 4 sheets-sheet 2 INVENTORMLM LSOAWN.

ug. 24, 1954 M D'AMORE 2,686,934

INJECTION MOLDING APPARATUS Filed July 7, 1949 4 Sheets-Sheet 3 5d do I,

INVENTOR Allg- 24, 1954 M. D'AMORE 2,686,934

INJECTION MOLDING APPARATUS Filed July '7, 1949 4 Sheets-Sheet 4 INJECTOR WROL VALVE INVBNTOR Patented Aug. 24, 1954 UNITED `STATES PATENTOFFICE INJECTION MOLDING APPARATUS Michael DAmore, Milwaukee, Wis.Application July '1, 1949, serial No. 103,481

(o1. liz- 30) 2 Claims.

. l This invention relates to plastic injectors for use particularly inthe injection molding of thermoplastics and the like.

Plastic injectors ordinarily comprise an elongated cylinder having adischarge nozzle at one end and a cooperating plunger operable to forcethe material through the nozzle into a mold.

The material is ordinarily supplied to the cyl` inder in loose granularor `powdered form and is there reduced to a plastic or fluid mass by theapplication of` heat as the material passes to and through the nozzleduring an injection stroke of the plunger.

As heretofore` designed, the capacity of a plastic injector is seriouslylimited by the amount of material that can be adequately fluidized orplasticized within the brief period of an injection cycle. This is 'duelargely to the nature of the materials commonly employed. Theyare liableto serious damage if subjected to temperatures above certain maximumsand also they offer very high resistance to the transmission of heat sothat heat penetration of the mass is most dinicult and time consuming.Yet it is essential to successful injection molding that every particleof material throughout the mass be raised to a fluidizing orplasticizing temperature before it leaves the injection nozzle.

The desirability and capabilities of my meri- "torious invention cangenerally be summarized in two words, capacity and time The capacity ofwhich my device is capable of delivering has never heretofore, accordingto my best knowledge and belief, been `approached by any other plasticinjector. Regardless of the fact that the capacity is greatly enlarged,I have `found it possible to deliver this greater mass to the mold in aminimum of time, less than the time required by the injectors indelivering far smaller loads. For example, by practising my invention, Ihave found that a mass Weighing approximately fifteen pounds can beinjected in a mold in less than six seconds.

One object of the present invention-is to'provide a thoroughly practicalplastic injector of greatly increased capacity.

A further object of the invention is providing an improved plasticinjector which is capable of injecting a greater mass by volume in amuch reduced period of time.

Another object of the present invention is to provide an improvedplastic injector in which the plastics are maintained free of entrainedair of other gases.

Other more specific objects and advantages will appear, expressed orimplied, from the following description of a plastic injectorconstructed in accordance with the present invention.

In the accompanying drawings:

Figure 1 is a vertical longitudinal sectional viewof a plastic injectorembodying the present invention.

Figure 2 is a longitudinal sectional View on a larger scale of theinjection nozzle shown in Figure 1.

Figure 3 is an end view of the injection nozzle.

Figure 4 is a longitudinal section view of a multiple injection nozzlethat may be substituted for that shown in Figures 1 and 2. l

Figure 5 is an end view of the multiple injection `nozzle shown inFigure 4.

Figure 6 is a diagram of a hydraulic system employed for `energizing theyplastic injector shown.

Figure '7 is a diagram of an electrical control system employed.

The plastic injector shown comprises an elongated injector cylinder I0supported in vertical end brackets II and I2 anchored to a suitablehorizontal bed plate I3. A piston I4 in the cylinder ID is actuated bythe ram I5 of a large hydraulic press cylinder I6 supported by end headsI'I and I8 `anchored to the bed plate I3. The injector cylinder Ill andpress cylinder I 6 are shown rigidly jointed through appropriate tierods I9.

The injectorcylinder IIJ is shown provided with a removable tubularliner 2U in which the piston I4 is closely tted, the liner 20 having aflange ZI at its rear end by which it is bolted or other- Wisedetachably xed to the rear end of the cylinder I0.

The piston I4 is preferably flexibly connected to the ram I5 in a mannerto compensate for any slight misalignment that may exist between theinjection and press cylinders I0 'and IB. For this purpose the rear endof the piston I 4 is bored to loosely receive a circular head 22 rigidlyfixed to the end of the ram l5. Two externally threaded rings 23,loosely encircling the .ram I5 and screwed into the piston I4, serve toIretain the head 22 against the base of the bore.

An additional heater in the form of a plug 26 is preferably provided atthe forward end of the injector with a circular series of narrowchannels 2l extending lengthwise therethrough and communicating with theinterior of the cylinder lil. The plug 28 is heated by athermostatically controlled electric heating element 28 of a well knowntype disposed within a longitudinal chamber 29 formed centrally of andwithin the plug and closed by a removable end cap 39.

In the injector shown in Figures 1, 3 and 4 the heater plug 26 providessupport for an injection nozzle 3l having a central longitudinal duct32' that communicates with the interior of the injector cylinder lethrough the several channels 2l' in the heater plug. The nozzle 3l isshown provided with a hollow tip 33 through which communication isestablished between the duct 32 and the receiving channel 34 of aconventional mold. The nozzle 3l is also heated preferably by a seriesof thermostatically controlled electrical resistors 35 disposed within acircular series of longitudinal bores formed therein.

- The duct 32 in the injection nozzle 3l is controlled by an appropriatevalve operable to open and close the same. A Valve for this purpose mayassume various forms but in this instance it comprises a longitudinallyreciprocable -plunger 36 that extends vertically through the nozzle 3land the duct 32. A spring 3l' reacts on the lower :t end of the plungerto lower the saine into ther position shown, in which position atransverse port 38 registers with the duct 32 to permit passage ofmaterial therethrough. A solenoid including a coil 39 coacts with theupper end of the plunger to elevate the same into a position where itblocks the duct 32. It will be readily appreciated by one skilled in theart that the plunger 35i may be hydraulically controlled.

Provision is made for supplying material in a hot plastic condition tothe injector cylinder ill preferably through the forward end of thelatter. Although mechanism for that purpose may assume various forms,that shown has proven quite satisfactory. This mechanism coinprises ahorizontal feed cylinder' lll which cornmunicates adjacent its rear endwith the discharge throat 4i of an appropriate hopper from which' coldmaterial in loose granuuar or powdered form may be admitted by gravityinto the feed cylinder. The feed cylinder d is in open communicationwith the forward end of the injector cylinder lli through a forwardextension t3 of the feed cylinder, through a heavy vertical conduit Allrigidly attached at its upper end to the extension 43 and at its lowerend to the injector cylinder l0, and through a port 45 provided in theinjector cylinder adjacent its forward end.

The forward extension 43 of the feed cylinder and the conduit 44 areboth externally and internally heated so as to thoroughly heat andlplasticize the material passing therethrough. In this instance externalheating is effected by the use of thermostatically controlled heatingunits 48 covered by appropriate shields 4l and i8 in much the samemanner as hereinabove described in connection with the injector cylinderEG. The feed cylinder extension 43 is internally heated by a heater plug49 having a thermostatically controlled electric heating element 5E)centrally disposed therein. The plug 49 is detachably fixed theextension 43 and is provided with a series of radial heating fins 5lextending lengthwise thereof and dividing the annular space between theplug /ii and extension 43 into a series of narrow channels through whichthe material passes in ytraveling from the cylinder 40 to the conduitdit. The conduit 413 is internally heated by a thermostaticallycontrolled electrical heating element E2 contained within a tubularhousing 53 that extends centrally through the conduit. The housing 53 issupported by an end head 5t screwed into the upper end of the conduittil and providing an end closure therefor'.

The feed cylinder d@ is preferably equipped with a water jacket 55 orother appropriate means for cooling that portion Vof the feed cylinderadjacent the hopper i2 so as to thermally isolate the same from theheated forward extension 43 of 'the feed cylinder and thereby avoidpremature heating of the material received through the hopper ll2.

A piston 5t closely tted for reciprocation in the feed cylinder e9serves a threefold purpose. It serves to initially ll the feed cylinderdil, the extension 23, the conduit it and the injector cylinder i9 withmaterial received through the hopper and to reiill the feed cylinderbefore each injection stroke of the injector piston Hl. For this purposethe piston 5d is caused torepeatedly reciprocate through a relativelyshort range beneath the hopper d2 so as to effect a pump-like action bywhich material intermittently received through the hopper is packed intothe cylinder lil and forced forwardly therethrough. The piston t alsoserves as a back stop to prevent reverse fiow of the material from theinjector cylinder it through the conduit ld, cylinder extension "i3 andcylinder 40 during the forward or injection stroke of the piston Thepiston 55 also serves to maintain the injector cylinder iii completelyfilled during the return stroke of the piston l 13 by advancing andforcing material'into the cylinder i@ as the piston Eil retracts. y

The piston 56 is actuated by the ram 5i' of a horizontal press cylinder58 which is rigidly connected to the rear end of the feed cylinder itthrough tie rods 59.

Both press cylinders i5 and 5t are energized hydraulicallyrby liquidreceived from an appropriate pressure source such as a conventional pump66.

The cylinder i6 is controlled by a three-position valve iii of a wellknown type controlled by two solenoids 52 and d3 as is illustrated inFigure 6. The valve 5i is spring centered so that it normally assumes anintermediate position in which the pressure supply pipe 6d is blockedand the pipes t5 and Se connected to the Vopposite ends of the cylinderi6 are both connected to the discharge pipe 6l. When one of thesolenoids S2 is energized, the valve 6| assumes one extreme position inwhich it connects the supply pipe 55 with the pipe Stand the pipe 5twith the discharge pipe fdl to effect retraction of the injector pistonand when the other solenoid 53 is energized, the valve Si assumes anopposite extreme position in which it connects the supply pipe dfi withthe pipe E@ andthe pipe @5 with the discharge pipe tl' to effect aforward stroke of the injector piston M.

In a similar manner the press cylinder 5.8 is controlled. by anautomatic two-position valve S3 of 12 is connectedto discharge pipe `14to effect a `forward stroke of the feed piston 56.

`A normally open valve 15 of a well known type controlled by a solenoid16 is included in the pipe 13. Whenever the solenoid 16 is energizeditcloses the valve 15 so as to block the iiow through pipe 13 andthereby hold the feed piston 56 against retractive movement. The severalsolenoids 62, 63, 69, 1E! and 16, as well as the solenoid 39thatcontrols the nozzle valve 356, are automatically controlled in a man nerto effect the desired sequence of operation of the injector piston I4,the feed piston 56, the

blocking valve 'I5 and the nozzle valve 36. An electric control systemwell adapted for the purpose is diagrammatically illustrated in Figure7. It is shown energized by the main electrical supply line 11-18. l

The feed piston 56 is controlled in its pumpn ing action by a detent 19carried by the press ram 51 and cooperating with two switch actuatingdogs 30 and 0I to normally limit the range of reciprocation of thepiston` 56. The dogs 8B and 8| are adjustably mounted on one of the tierods 59 within the path of travel of the detent 19.

The dog 80 controls two integrally connected switches 82 and 83contained in separate lines 84 and 85, respectively. A spring 86 urgesswitch 82 toward open position and switch 63 toward closed position, butthe detent "I9 acts on the dog 80 to close switch 92 and to open switch83. Similarly the dog 8| controls a normally closed switch 8l' intheline 84 and an integrally connected normally open switch 68 in the line85. The solenoid 'I0 is controlled by the line 84 which is connectableto the main line 11 through a manually controlled main switch 89.Similarly, the solenoid 69 is controlled by the line `85 which, when themain switch 89'is closed, is normally connected to the main line 11through a normally closed switch 90 and lead 9|.

The arrangement is such that when the switch 09 is closed, the ram 51and feed piston 56 reciprocate continuously within a range determined bythe spacing of the dogs and 9|.

That is to say, when the piston`56 and ram 51 reach the end of theirreturn stroke, the detent 19 acts on the dog 80 to close 4the switch S2and open switch 83, whereupon the solenoid 10 is `excited and the valve68 shifts to effect a forward stroke of the ram 51 andpiston 56;thereafter, as the ram 51 advances the switch 83 closes and the switch82 opens under the action of the spring 66 so that the solenoid 16 isdeenergized, and the `valve 08 retains its position until the detent 'I9strikes the dog 8|; thereupon the detent I9 acts on the dog 6| to openthe switch 81 and to close the switch S0 to thereby energize thesolenoid 69 and cause the valve 68 to shift intoposition to eiect areturn stroke of the `ram 51 and piston 56. It will of course beunderstood that during each return stroke of the piston 56 a charge ofmaterial enters the feed cylinder through the port 4I, and that duringeach advance stroke of `the piston 56 the chargeof material thusadmitted is advanced forwardly into," the cylinder 40. This action`continues until all of the spaces withinthe cylinder 40, conduit 44,and injector cylinder II) are completely filled and until the piston56`stalls against the resistance of the ma- -terial thus packed therein.

Throughout this reciprocating or pumping action of the piston 56 theinjector piston I4 remains in the retracted position shown in full linesin Figures 1 and 2, and the nozzle valve 36 is retained in its upperclosed position by the solenoid 39 normally energized from the main line'I1 through a normally closedswitch 92 contained in 4 the lead 93. i

The retracted position of the injector piston I4 is determined by adetent 94 adjustably xed to the ram l5 and cooperatingwith aswitchactuating dog 95 fixed to the end head I1 of the press cylinder IS. Aswitch 96, normally closed by a spring 91, is opened by the action ofthe detent 94 upon the dog 95 to terminate the return stroke of theinjector piston |4 in a manner to be later described. f

After the feed piston 56 has stalled aga-inst the material in thecylinder 40, a` forward injection stroke of the injector piston I4 isinitiated by the momentary closing of a manuallycontrolled normally openswitch 98 contained in a line 99 extending4 from the main line 11 andleading througha normally closed switch |00 to the solenoid coils |0I,|02, and |03 of three separate relays. Upon closing the switch 98, twoof the coils I0! and |02 are instantly energized but, for rea sons thatwill hereinafter appear, the third coil |03 is not energized until apredetermined period thereafter, an automatic timing device |04 beingincluded in the circuit to efect the desired delayed action of the coilI 03.

When energized, the coil IOI closes three normally open switches |05,|06 and |01 and opens,

switch |08. The closing of switch |01 energizes the coil |09 of a fourthrelay through a lead IIil from the main line 11 through a normallyclosed manually operable switch III. When the relay coil |09 isenergized, it functions to close four normally open switches H2, |I3,`II4 and ||5. The switch |05 functions as a holding switch for the relaycoils |0I, I 02 and |03, all being locked in through a lead I|6 from theline 9|, through switch |05 and a lead III to and through a normallyclosed switch IIB and a lead I9 which contains the switch I I5 (thenclosed by the relay coil |89) andwhich is connected to the line 99leading to the relay coils |0I, |02 and |05 The relay coil IGI thusremains energized until the switch I I8 is opened by the relay coil |03or until the switch H5 is reopened by deenergization of the relay coil|69. Also the relay coil |09 is locked in through a lead |29, holdingswitch II4 and lead |2I to the coil |99, so that the relay coil |99remains energized so long as the normally closed manually operableswitch III remains closed. l l

When the switch |06 is closed by the relay coil IiiI, the solenoid 63 isenergized through leads I I0 and |22 so that the injector control valve6I is shifted and the injector piston I 4 starts a forward injectionstroke. At the same time the switch 92 is simultaneously opened by thesimultaneously energized relay coil |02, so that the `solenoid 39 isdeenergized and the nozzle valve 35 'vents escape of material th-roughthe port45 from theinjector cylinder lirsothat sufficient pressure maybe developed in the cylinder l0,v to insure rapid discharge through thenozzle 3|.

The, injection. stroke of the piston I4 continues untilr the mold 344 iscompletely filled with material supplied through the nozzle 3| until thepiston |4 stalls against the back pressure of the material in thefilled' mold and there it remains fora short dwell., determined by thetiming device |64'. The device |64 is set to delay energization of. therelay coil |03. until a` predetermined period of time after the relaycoil IDI was energized, the time period being' somewhat greater than thetime required for the piston I4 tov complete its injectionl stroke. Atfthe end of this time period (including the piston dwell) the relay coil|63 functions to open thel switch IIB and thereby deenergize therelaycoils I|l| and |62A by disconnectingleads I-|6 and |I'|' from thelead I |53.

Deenergization of the relay coil |62 closes the switch 9-2' so thatthesolenoid 39 is again energized and the nozzle valve 36 closed.

Deenergization of the relay coil |6| opens the switch |66 to therebydeenergize the solenoid 63 and permit the injection control valve 6I toassume its intermediate. position and thus neutralize the press cylinderI6, and also to deenergize the solenoid 'I6 so that the valve 'l5 opensand exposes the feed cylinder 58 to the pressure in the pipe I3 totherebycause the feedY piston 56 to continue its advance against thematerial in the feed cylinder 40'. This continued advance of the feedpiston 56 forces the material through the cylinder 40' and conduit 4'4intothe cylinder I6 to maintain the cylinder I6 nlled during retractionof the injector piston |4.

Also when the relayv coil ||I| became deenergized, the switch |08closed, thereby energizing the coil |23 of a fifth relay through a lead|24, switch |06-, lead |25 (containing the then closed switch 96),switch |I3 (then closed by relay coil |691) and lead |26 from lead 9 I'.Energization of the relay coil |23 effects energization of the solenoid62' through a lead |21, switch |23, and leads |1291 and' ||6 from themain line ll, so that the valve 6| then shiftsl into position to supplypres# v sure to the forward end of the press cylinder I6 and thus effectretraction of the piston I4 by the action of the press cylinder.

Under some conditions oi'l operation it is desirable to effectretraction of the piston I4 solely by the thrust of the material forcedinto the injector cylinder |*IJ by the action of the advancing feedpiston 56. operable switch |30 is included in the lead |21 which, whenopen, will prevent energization of the solenoid 62` and thus permit thevalve 6| to remain in its intermediate position during the advance ofthe feed piston 55.

Itis important at this stage of the cycle that the switch 88v berendered ineffective to interrupt the advance of the feed piston 56 whenthe detent I3 on the advancing ram 5l engages the dog 6|. This isaccomplished by placing the normally closed switch 9,0 under the controlof relay coil |23, so that when the latter is energized,y the switch 90opens and separates the leads 65 and 9|, thereby preventing energizationof the solenoid 69 when the switch 88 closes. Due to this arrangementthe feed piston 56 continues to ad- Vance until the injector piston I4reaches the end of its returnstroke.

When the injector piston I4 reaches the end `of Vits return strokev itcomes to rest and the feed For this purpose a manually piston 56 beginsa return stroke by reason of the controls now to be described. When therelay coil 23 became energized by deenergization of the relay coil IOIthe coil |23 closed a switch |3| which functioned to energize a coil |32of a sixth relay through a lead |33, switch |3I, and a lead |34connected with the energized lead I9, the lead |34 containing a normallyclosed switch |35 controlled by the coil |36 of a seventh relay. Therelay coil |32 is locked in by a holding switch |31 which when closedconnects the leads |34 and |33. A normally open switch |38 closed byenergization of the relay coil |32 is operable to connect lead |25 witha lead |39 which is'connected through the normally closed switch 83 withthe solenoid 69 of the feeder control valve 63. The lead |39 contains anormally closed switch |40 openable by energization of the relay coil|23'.

By virtue of the arrangement just described both of the relay coils |23and |32 remain energized until the lead |25 is broken by the opening ofswitch 96, which of course occurs when the dog 65 is actuated by thedetent 94 on the ram |5 as the injector piston |4 approaches the end ofits return stroke. The opening of the switch 96 effects deenergizationof the relay coil |23, causing the switch |28 to open and to deenergizethe solenoid 62, whereupon the-injector control valve 6I assumes itsintermediate neutral position and the injector piston |4 cornes to rest.Deenergization of the relay coil |23 also causes the switch |46` toclose and to thereby energize the solenoid 69 through the lead |26,switch H3, lead |25, switch |36, lead |39, and the then closed switch83. The solenoid 63 then functions to shift the feeder control valve|53l into a reverse position so as to elfect a return stroke of the feedpiston 56.

When the switch 93 opens under the action of the detent 94 upon the dog35, a second switch |4I connected therewith closes and thereby connectslead I25witha lead |42 leading to the relay coil |36 and also to thecoil |43 of an eighth relay. The action of both coils |36 and |43 aredelayed by separate timing devices |44 and |45 of a well known typesimilar to the timing device |64 hereinabove mentioned.

The timing device |44 is set to delay action of the relay coil |36 for apredetermined period of time after the switch 66 opens, the time periodbeing of such length as to permit the detent 19 on the ram 51 to pass,the dog 8| during the return stroke of the feed piston 56. At the end ofthis period the relay `coil |36 acts to open the normally closed switch|35 to thereby effect deenergization of the relay coil |32, it beingunderstood that the holding switch` |31 is effective to lock in the coil|32 only while the switch |35 is closed. The switch |33 controlled bythe coil |32 then opens and renders the lead |39 ineffective on thesolenoid 69. Thereafter the feed piston 56 responds to the action of thedetent 19 upon the switch actuating dog 8|) and 8| and reciprocates backand forth beneath the hopper port 4I `to again pump loose material intothe cylinder 46 in the manner hereinabove described.

The timing device |45 is set to delay action of the relay coil |43 for apredetermined time period after the switch 96 has been closed by thereturn stroke of the injector piston I4, the time period being such asto permit the feed piston 56 tol-complete its pumping action and toagain dwell against the back pressure of the material in the lled feedcylinder 40. When the coil |43 acts,

it closes a switch `|46 and thereby reenergizes the relay coils I I, |02and |03 by connecting them to the energized lead 9| through lead |41,switch |46, lead IH, switch IIB, lead |I9, switch (the 'coil |09 beingstill locked` in), and lead `99. These relay coils are thusautomatically reenergized to start `a new cycle without requiringanother manual closing of the starting switch 98, the new cycle being arepetition of `that above described and being `automatically renewedeach time that the relay coil |43 acts to close the switch |46.

During the beginning of each cycle, when the injector piston I4 startsan injection stroke, the.`

detent 94 onthe ram I5 releases the dog 95 and the switch |4| opens,thereby disconnecting the lead |42 from the energized lead |25 anddeenergizing `both of the relay coils |36 and |43 so that the switchassumes its normally closed position and the switch |46 assumesitsnormally open position. H

Each cycle terminates with the injector piston I4 and its rarn l5 inretracted position and `with the switch I4I held closed by the detent 94and coacting dog 95. With the parts thus positioned, l

the lead |42 to the relay coils |36 and |43 is connectable to the livewire 9| through the switch I |3, so that their timing devices I 44 and,|45 are liable to be prematurely energized by the initial energizationof the relay coil |09. It will be remembered that the relay coil |09 isinitially energized when the switch 98 is manually closed, so thatunless provision were made to prevent it, prematureenergization of thetiming devices |44 and |45might occur. To avoid this a normally closedswitch I 49 is included in the lead I 42, this switch being connected tothe switch 98 so that, whenever the latter is closed to initially starta cycle, the switch |49 automatically opens to break the lead |42 andthus prevent energization of the timing devices |44 and |45 at thattime.

It will thus be noted that mechanism has been provided for lling aninjector cylinder |0 with hot plastic material while the injector pistonI4 is in retracted position, this being eifected by the pumping actioncfa piston 56 reciprocating beneath the outlet 4| of a supply hopper 42in a manner to force successive charges of material received from thehopper through a feed cylinder 40, extension 43, and conduit 44. As thematerial advances through the cylinder extension and conduit 44 it isthoroughly heated to a predetermined plasticizing temperature byexternal heaters 45 and by internal heater plugs 49 and 53 through oragainst which the material passes in its travel toward the injectorcylinder.

It will be further noted that the mechanism described includes means forsecurely holding the hot plasticized material against back flow from thecylinder I0 as the injector piston I4 advances on an injection stroke,so that this material can escape only through the injection nozzle intothe mold 34. This is effected by blocking escape ofliquid from the presscylinder 59 in such manner as to lock the feed piston 56 againstretraction under the high back pressure of the material within theconduit 44, cylinder extension 43 and cylinder 40.

,It will also be further noted that in the mechanism described provisionis made for maintaining the injector cylinder |0 completely lled withhot plasticized material during the return stroke of the injector pistonI4. This is made possible by the fact that the material enters thecylinder I0 from adjacent the front end thereof and is actually effectedby causing a continuous advance of the feed piston 56 while theinjectorpiston I4 is retracting.

In this connection it is pointed out that in the injector shown theinjector piston I4 never advances beyond or closes the inlet port 45 ofthe injector cylinder I0, so that no partial vacuum or empty pocket isformed ahead of the inlet port such as so commonly occurs during thereturn stroke of the injector plunger in injectors heretofore used. Theelimination of such a vacuum or empty pocket is highly advantageous inthat it avoidsall danger of admitting air to the plastic material,entrained air being a common cause of defective molded products.

It will also be further noted that in the mechanism described provisionis made for adjusting the stroke of the injector piston I4 so as toadapt the amount of material injected during each cycle to the capacityor requirement of the particular mold. This is effected by adjustmentofthe detent or collar 94 upon the injector ram. By adjusting the collar94 to a position further from the piston I4, for instance, the collar 94will engage the switch actuating dog 95 at an earlier point in thereturn stroke of the piston I4 and thus reduce the effective stroke ofthe piston I4 and correspondingly reduce the amount of material suppliedto the injector cylinder l0 during each return strokeof the piston I4.The functional eiect of such an operation is unique and should beappreciated. Thereby the injector may emit a mass varying in weight froman ounce to over fteen pounds.

In spite of the common practice of heating the nozzles of plasticinjectors, it not infrequently happens that the material in the nozzle,and particularly in the tip end thereof, becomes chilled and forms asolid slug the removal of which, though diiiicult, is necessary forsuccessful injection. In the injector shown provision is made for thequick and easy removal of such slugs, the valve 36 being utilized forthat purpose. In this instance a port |50 is formed in the side of theplunger 36 in position to register with the discharge end of the nozzleduct 32 when the plunger 30 is elevated to the valve closing position. Ahose I5| leading from a suitable source of air pressure communicateswith the port |50 through a longitudinal duct |52 formed in the lowerend of the plunger 36. The arrangement is such that by lifting theplunger 36 into valve closing position, a blast of high pressure air maybe delivered from the hose I5| through the port |50 to force the outerend of the nozzle duct 32 clear of any material contained therein.

The injector hereinabove described is of a capacity several timesgreater than injectors heretofore used, this greater capacity being madepossible by the fact that the material is delivered to the injectorcylinder I0 in a hot and thoroughly plasticized condition. Because ofthis increased capacity, an injection nozzle 3| having a plurality ofdischarge ducts 32 may be advantageously employed, particularly when theinjector is being used at maximum capacity. Such a nozzle, shown inFigures and 6, is otherwise similar to the nozzle 3| hereinabovedescribed and may be used in place of the latter.

The nozzle shown at 3| is provided with two discharge `ducts 32' bothcommunicating with the interior of the injector cylinder throughchannels 2l in theheater plug 26, but each being equipped with aseparate discharge nipple 33' through which the plastic material isforced into separate intake channels 34 in the mold. The fact that thematerial .enters the mold through separate channels 34 is highlydesirable in that it facilitates prompt distribution of the materialthroughout the .mold cavity, a condition that is quite advantageousparticularly when the mold cavity is of large capacity, .extended over alarge area, or composed of an .intricate network of narrow channels andpockets .as is `so commonly the case.

In this instance both ducts 32 are controlled by a single cut-off valvein the form of a reciprocable plunger 36' extending through both ducts32 and having .two transverse passages 38 each adapted to register withone of the ducts 32 when the plunger 36 is lowered into the positionshown. When .raised toa position where the passages 38 'are out oi linewith the ducts 32', they plunger then blocks both ducts. The plunger 38is operated and controlled in the .same manner as above described inconnection with the cut-oil valve 36 of nozzle 3|. The plunger 36 isalso shown equipped with two air .ports |50 connected through achannel152 with an air pressure hose [5V by which the ducts 32 may be clearedof material lodged therein in the manner as above described.

The nozzle 3l is heated in 'much the same manner as nozzle 3| byelectric heating elements 35' aranged at opposite sides yof each duct 32and by an additional heating element 35 arranged between .the 4ducts32'.

Various changes may be made in the embodiment of the inventionhereinabove specifically described Without departing from or sacricingthe advantages 'of the invention as dened in the appended claims.

I cla-im:

1. A plastic injector lcomprising an injector erable to force materialfrom said cylinder through said nozzle, means in continuouscommunication with said rcylinder for supplying material to vsaidcylinder to ll the latter during each reimrn stroke of said plunger,means adjustable to regulate the return stroke of said plunger tothereby regulate the amount of material contained in said cylinderbefore each working stroke of 4said plunger, means lcooperating withsaid supply means for heating said material to plasticize the samebefore admission thereof to said cylinder, and means cooperating withsaid cylinder 'to force material therefrom through said nozzle, andmeans for eject'ing material from said passage, said last-named meanscomprising means for directing a fluid pressure medium outwardly through.said'passage to .clear the same.

References cited in the fue of this patent UNITED srA'rEs PAfrEN'rs

